Facebook now lets you announce whether you're an organ donor. It's not a substitute for registering in your state, but donor advocacy groups hope more people will become donors once they see their Facebook friends doing it.

On Tuesday, Facebook announced a new feature that lets users designate their organ donor status and directs them to a donation registry page. Here, Mark Zuckerberg takes questions from the media during an event at Harvard University in Cambridge, Massachusetts.

Facebook teased Monday that it was working on a feature that had "the power to save lives." Now they've taken the wraps off a new feature that, while slightly unusual, certainly makes good on that promise: an organ-donor status option. Facebook announced the move Tuesday morning, adding that it's designed to shorten or eliminate organ-transplant waiting lists.

Facebook users in the US and UK can now choose to indicate that they're organ donors, as well as specify which state they're registered in, post a message explaining why they became a donor, and give the date they registered in their state.

A Facebook status isn't a substitute for traditional consent (don't worry -- a doctor couldn't harvest a patient's organs after checking their Facebook profile). But the status option is designed to spread awareness among other Facebook users, as well as to let family members know about one's status in case they ever need to give consent. Facebook also provides a link to state organ donation registries, for those who want to be donors but didn't sign up when they got their driver's license.

Is it working? Forbesreports that organ donor designations in California are way up already -- 550 online designations by Tuesday afternoon, compared with about 70 in a normal day. And the New York Timesquotes a transplant surgeon's estimate that "millions" of people could designate themselves as donors in the next few days.

The peer-pressure approach to organ donation could make a big difference: as awareness and publicity increase, the ranks of willing organ donors could grow correspondingly. The Times adds that almost 7,000 Americans die each year waiting for organ transplants to become available, so doctors consider a greater number of registered donors to be a good thing.

Facebook made the signup process easy. Just go to your Timeline, click the "Life Event" button next to the status bar, and select "Health and Wellness." An organ donation option should pop up, letting you select your status and providing a link to the organ donation registry in your state.

Of course, Facebook is no stranger to privacy concerns -- and the company is certainly breaking some new ground by asking for data about its users' health records.